Shadows of Venus

November 28, 2005: It's often said (by astronomers)
that Venus is bright enough to cast shadows.

So
where are they?

Few
people have ever seen a Venus shadow. But they're there, elusive
and delicate—and, if you appreciate rare things, a thrill
to witness.

Attention,
thrill-seekers: Venus is reaching its peak brightness for
2005 and casting its very best shadows right now.

Above:
Venus at the beach on Nov. 19th. There are no Venus shadows
in this particular photo, only reflections. Credit: Pete Lawrence.

Amateur astronomer Pete Lawrence of Selsey, UK, photographed
the elusive shadow of Venus just two weeks ago. It was a quest
that began in the 1960s:

"When
I was a young boy," recalls Lawrence, "I read a
book written by Sir Patrick Moore in which he mentioned the
fact that there were only three bodies in the sky capable
of casting a shadow on Earth. The sun and moon are pretty
obvious, but it was the third that fascinated me -- Venus."

Forty
years passed.

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Then,
"quite by chance a couple of months ago," he continues,
"I found myself in Sir Patrick's home. The conversation
turned to things that had never been photographed. He told
me that there were few, if any, decent photographs of a shadow
caused by the light from Venus. So the challenge was set."

On
Nov. 18th, Lawrence took his own young boys, Richard (age
14) and Douglas (12), to a beach near their home. "There
was no ambient lighting, no moon, no manmade lights, only
Venus and the stars. It was the perfect venue to make my attempt."
On that night, and again two nights later, they photographed
shadows of their camera's tripod, shadows of patterns cut
from cardboard, and shadows of the boy's hands—all by the
light of Venus.

The
shadows were very delicate, "the slightest movement destroyed
their distinct sharpness. It is difficult," he adds,
"for a cold human being to stand still long enough for
the amount of time needed to catch the faint Venusian shadow."

Difficult,
yes, but worth the effort, he says. After all, how many people
have seen themselves silhouetted by the light of another planet?

If
you'd like to try, this is the week. Your attempt must come
before Dec. 3rd. After that, the crescent moon will join Venus
in the evening sky, and any shadows you see then will be moon
shadows.

.
When the sky fades to black, turn your back on Venus (otherwise
it will spoil your night vision). Hold your hand in front
of a white screen—e.g., a piece of paper, a portable
white board, a white T-shirt stretched over a rock—and let
the shadow materialize.

Shadows
or not, before you go home, be sure to look at Venus directly
through binoculars or a small telescope. Like the moon, Venus
has phases, and this week it is a lovely crescent. Aside:
If Venus is at peak brightness, shouldn't it be full?
No. Venus is full when it is on the opposite side of the sun,
fully illuminated yet far from Earth. Venus is much brighter
now, as a crescent, because Earth and Venus are on the same
side of the sun. Venus is nearby, big and bright.

Hey
wait a minute! Technically speaking, Venus
will be brightest between Dec. 8th and 15th. But Venus
is about as bright now as it is going to be then. From
Nov. 28th to Dec. 3rd is the best time to look for Venus
shadows, because during that interval the moon will
be absent from the evening sky. After Dec. 3rd, you'll
be observing moon shadows.